Producing aluminum fluoride-alkali-metal fluoride double compounds practically free from iron



Patented Wee. 2, lld dl.

HEINRICH SPEGKETER, OF GRIESHEIM-ON-THE-MAIN, JULIUS SCSLL, OF SCHWAN- HEIM-ON-THE-MAIN, AND ROBERT BILFINGER, OF GRIESHEIM-ON-TI'IE-MAIN', GEE,- MANY, ASSIGNORS TO THE CHEMISCHE FABRIK GRIESHEIlVl-ELEKTRON, OF FRANK- FQRT-ON-THE-MAIN, GERMANY.

PRODUCING ALUMINUM FLUORIDTE-ALKALLMETAL FLUORIDE DOUBLE COMPOUNDS PRAGTICALL'Y FREE FROM IRON.

No Drawing.

To all whom it may conccwt.

Be it known that we, IIEINRICH Srnoun 'rnn, a citizen of Germany. and residing 'at Griesheinron-the-Main. Jumps SULL, a citizen of Germany. and residing at Schwanheim-on-the-Main, and ROBERT Binrixonn. va citizen of Germany, and residing at Griesheimbathe-Main, Germany. have invented certain new and useful Improvements in Producing Aluminum Fluoride Alkali-Metal Fluoride Double Compounds Practically Free from lron, of which the following is a specification. I

The present invention relates to the production of aluminum-alkali-metal fluorides of the chiolithe or kryolithe type or of mix tures thereof which may be used in the manufacture of aluminum or aluminum saltsin 'a similar manner as pure kryoli'the.

We have found that aluminum-alkalimetal double salts of high pureness and especially practically free from iron are obtained from aluminum salts (especially from the productsresulting from theextraction of argil or potters earth with mineral acid) by treating the acid aluminous solutions after having filtered off the silicious residue with an akali-metal salt and hydrofluoric acid or with mineral acidsand alkali-metal fluorides under such conditions that the iron salt present remains inert against fluorides. One method of precipitating the aluminum whilst keeping the iron salt inert, that M is to say dissolved, has proved to consist in employing only such a. quantit of hydrofluoric .acid that just a little hit of unchanged aluminum salt in addition to the iron salts remains dissolved, so that the solution filtered ofi from the precipitate contains more aluminum salt than the percentage correspondingto the solubility of the aluminum'alkali-metal double fluorides.

Another method of making the dissolved iron salt inert against hydrofluoric compounds consists in reducing to ferrous compounds the dissolved ferric salts, for instance by means of sulphuretted hydrogen. In this case fiuoric compounds may be added to any amount Without contaminating with iron the products obtained.

its to the addition of alkali-metal s alts Application filed September 1, 1923. Serial No. 660,636.

there is no restriction. An alkali-metal salt of the acid which has served for extracting the alun'unous ore may be used or an alkalimetal salt of another acid. By the action of the hydrofluoric acid the mineral acid is recovered in the filtrate. as far as it was c0mbined with the aluminum and akali-metal precipitated or added in excess. and this mineral acid either mixed or uniform may be used without further treatment for extracting new quantities of pott fs earth. In order to avoid more mineral acid being formed by the action of the hydrofluoric acid than required for the extraction of the aluminous ore alkali-metal 'fiuoride may be wholly or partially substituted for alkalimetal choride or sulfate.

To obtain a maximum yield of hydrofiuoric compounds also the alkali-1netal salts may be added in excess. This excess will not be lost as the salts passing into the filtrate are serving for the benefit of the next extraction.

After repeated use of the filtrate for extracting new quantities of potters earth the iron will be progressively enriched in the solution, but this fact does not injure the quality of the aluminumalkali-metal double fluorides obtained provided that'the precise conditioiis explained in the following examples are observed, even if a larger quantity of iron than of aluminum is already present.

Ewample 1.

heating is still. continued for about 15 minutes to complete the precipitation of the aluminous compounds. The well filterable precipitate is sucked oii in the heated state and Washed out. It forms an aluminumsodium fluoride which is practically free from iron.

The process may be modified in that the solution of common salt is first added to the aluminum salt solution and then the precipitation with hydrofluoric acid is oftected. In this case care must be taken for eflicacious stirring during the addition of the hydrofluoric acid in order to avoid any local excess of hydrofluoric acid in the reacting mixture as the iron salt would not be inert against such an excess and would be precipitated.

kilograms of sodium chloride dissolved in 250 litres of water are added to 200 litres of filtrate from the extraction of argil or potters earth with hydrochloric acid. Hereupon the iron oxide salt is reduced to the ferrous compounds, e. g. by introducing .sulphuretted hydrogen into the solution. Then the solution is heated to its boilingpoint and 250 kilograms of a 20 per cent hydrofluoric acid solution are added. After sucking off and washing the product is practically tree from iron.

Emdmple 5.

500 kilograms of a 20 fluoric acid solutionure ad of a solution containin A1 0 and 16.0 gramsoi e 0 per litre in the form of sulfates. The solution is heated to boiling and a hot solution of 170 kilograms of common salt in 500 litres of water is added. The precipitate of double compounds atter washin and drying contains only traces of iron. the filtrate is forming a mixture or" hydrochloric and sulphuric acid which may again be used for extractor beat hydroded to 500 litres 90.6 grams of lit it is desired to avoid such mixtures the ferric compounds may be reduced to the ferrous form and then the practically pure aluminum double fluorides precipitated by sodium sulfate according to the following Example 4.

In 200 litres of a solution containin 90.6 grams of A1 0 and 16.0 grams of a0 per litre in the form of sulfates the iron oxide is reducedto ferrous oxide by means of sulphuretted hydrogen. Then under stirring and heating a hot solution of,80 kilograms of sodium sulfate in 200 litres of Water and 250 litres of a 20 per cent hydrofiuoric acid are added. After sucking oil and Washing the double compound produced will contain only traces of iron.

The sequence of, the additions of alkalimetal sulfate and hydrofluoric acid may be exchanged Without the result being affected.

However it may be desirable in some cases to operate inversely with hydrochloric or sulfuric acid and alkali-metal fluorides instead of hydrofluoric acid and alkali-metal chloride or sulfate; this is especially the ei-races case when sodium fluoride is to be regenerated from double fluorides (ii the latter are employed).

Example 5.

Example 6.

200 litres of hydrochloric acid extract as in the foregoing example are llfillttlfil to 70450 degrees centigrade. and a solution of 90 kilograms of sodium fluoride in 150 litres of concentrated hydrochloric acid is slowly introduced under stirring. The stirring is continued for a short time and the precipitate is sucked oil.

The operations are susceptible of various other changes and modifications without departing from the spirit of the invention. Such for instance, the hydrofluoric coinpounds may he slowly added, the mixture digested for a While, and finally the alkalimetal salts may be added. Or one hall of the hydrofluoric compounds may be added,

the mixture may be digested for a while, and finally the restof the hydroliuoric compounds and the alkali-metal salts may be added.

. 1. Process for producing aluniimmi-alIrali-mctal double fluorides practically tree from iron, consisting in precipitating under stirring the said double fluorides from aluminum salt solutions containing. iron by the addition in presence oil free mineral acid, of substances which on dissolvingin water form fluorine ions and allmli-motul. ions, the said precipitani's being added to such an extent that just a little bit of unchanged aluminum salt is left in solution.

2. Process for producing aluminum alkalisinetal double fluorides practically free from iron, consisting in precipitating under stirring the said double fluorides from aluminum salt solutions containing; iron by the addition of hydrofluoric acid and alkali-metal salts in presence of free -mineral acid, the said hydrofluoric and 111' under stirring the said double lluorid a from aluminum chloride solutions containing iron by the addition of hydrofluoric acid and. olhall-metal salts in presence of ree iniueiul lilii immune 7 inc ssid hydrofluoric acid and ulltalisslts: locing added to such an extent 1st at little bit of unchanged aluminum is is loft in solution.

' occss for producing aluminum e1 double fluorides practically free ron consisting in precipitating under 3; the said double fluorides from ninum chloride solutions containing iron the addition of hydrofluoric acid and al- .-iete.l sulfate in presence of free mineral com the said hydrofluoric acid and ellnilinietul siflfotc loein udded to such an extent that just c litte bit of unchanged aluminum chloride is left in solution.

5. Process for producing nluminuln-al iozrli-metsl double fluorides from, iron, consisting in preci itating under stirrii-ig the said double uorides from i minum suit solutions contoining iron by Wly adding, in presence of free mineral Tlrydrofiuoric compounds, digesting the turn for a While, and finally under constirring ridding alkali-metal salts, the wmity of tlic precipitating agents being csiculutcd in such manner that just it little bit oi unchanged aluminum salt is left in solution.

6. Process for producing aluminum-ai- 'mctsl double fluorides racticelly' tree iron, consisting in arccrpituting under stirring the said doulo e fluorides from racticully free aluminum salt solutions containing icon by slowly adding, in presence oi free mineral acid, hydrofluoric acid, digesting; the mixture for a while and finally under continucd stirring adding alkali-metal salts, the quantity of the precipitating agents locin culcuieted in such manner that just a, 11 c loit of unchanged aluminum salt is left in soiu tion.

7. Process for producing aluminum-ab kali-mctal double fiuoridcs from iron, consisting in precipitating; under stirring the said double fluorides from aluminum salt solutions containing iron by slowly adding, in presence oil free minerul acid, only half of the hydrofluoric con1- pounds required, digesting the mixture for a While, and finally adding the rest of the ructicslly free hydrofluoric compounds and the alkali-metal salts, the quantity of the prccipitsnts lacing calculated in such manner that just as little bit of u ncha nged aluminum salt is left in solution.

In testimony whereof We afix our signattures in presence of two Witnesses,

HEINRICH SPJEGKETER. JULIUS SGLL. ROBERT BILFINGER. Witnesses:

Goons Enunszur, 

